Matthew 19:6-9 NIV

6 So they are no longer two, but one flesh. Therefore what God has joined together, let no one separate.”
7 “Why then,” they asked, “did Moses command that a man give his wife a certificate of divorce and send her away?”

References for Matthew 19:7

8 Jesus replied, “Moses permitted you to divorce your wives because your hearts were hard. But it was not this way from the beginning.
9 I tell you that anyone who divorces his wife, except for sexual immorality, and marries another woman commits adultery.”

References for Matthew 19:9